1. Field of the Invention
The present invention relates to a power saving diversity mode wireless LAN mobile communication device.
2. Description of the Related Art
A communication system using diversity mode wireless LAN terminals is shown and described in Japanese Patent Publication P2000-13393A. In this prior art system, a wired LAN terminal and a wireless LAN terminal. Each terminal is provided with a pair of diversity antenna systems to establish a wireless link The wired LAN terminal is an access point of the wireless LAN terminal to a LAN cable. A desktop computer is connected to the wireless LAN terminal. One of the wireless links is used as a working transmission system and the other as a spare or backup transmission system. When the working transmission system fails to meet a specified bit error rate, protection switching occurs between the working and backup systems. Since the wireless LAN terminal is a fixed terminal, the backup system is constantly warmed up by the mains power supply in readiness for protection switching. However, a substantial amount of power is dissipated when the spare unit is being warmed up.
In the case of a wireless LAN cellular mobile terminal that establishes a session with a remote terminal using a wireless link to a base station, it is necessary to periodically perform handover from one base station to the next when the session proceeds as the terminal is on a vehicle travelling at high speed. To ensure against interruptions, the diversity method is advantageous for the wireless LAN cellular mobile terminal since it allows one of the transmission systems to operate for establishing a session with a base station and allows the other transmission system to operate for making a search for the next base station while the session proceeds. However, due to the limited battery power, the diversity mode wireless LAN cellular mobile terminal would encounter difficulty in continuing a session for an extended period of time.
A power saving diversity mode wireless communication device is disclosed in Japanese Patent Publication 1996-107381. According to the prior art, a plurality of wireless interfaces are set in a power-ON state and one of the wireless interfaces is selected to establish a channel with a remote terminal and the quality of the channel is monitored. When the monitored quality of the channel is higher than a threshold value, the other wireless interfaces are set in a power-OFF state. If the quality of the channel drops below the threshold value, the other wireless interfaces are set in a power-ON state and the same process is repeated.